Many respirators that are sold today use a thin rigid structural part for attaching filter elements and valves to the mask body. These rigid structural parts are commonly produced through injection molding and are often referred to as a “nosepiece” or “rigid insert”. A soft compliant material, which conforms to a person's face, is disposed on or about the rigid structural insert to enable the mask to fit snugly over the wearer's nose and mouth. The use of a rigid insert in conjunction with a soft compliant portion tends to make the mask lighter and more comfortable to wear, particularly when compared to previous masks that had used thick rubber throughout essentially the whole mask body to support the filter cartridges and valves. Examples of masks that use a rigid insert in conjunction with a compliant face-contacting member are shown in U.S. Pat. No. 6,016,804 to Gleason et al., U.S. Pat. No. 5,592,937 to Freund, and U.S. Pat. No. 5,062,421 to Burns et al.
The rigid structural components that are employed in mask facepieces regularly incorporate multiple integrated elements that have distinct dimensional tolerance requirements and complex shapes that are customarily formed in molds at relatively great expense.
The control of dimensional tolerance—including actual dimension and conformation of an injected molded part—can be affected by the material used, the cycle time of the part, the mold configuration, and the part design. For a given material and a given part design, the factor that limits production typically is related to the element that has the greatest tolerance requirement. Higher tolerance parts, more-often-than-not, require additional oversight and technical expertise to correctly manufacture.
To properly utilize the efficiency and accuracy of injection-molding technology, designers have sought to encompass as much detail as possible in the molded part so that the whole rigid structural insert can be manufactured in one step. The result therefore often involves complex tooling that is difficult to maintain and operate, especially when used in remote facilities that do not have access to well-trained technical resources. Thus, the higher tolerance requirements for certain portions of the rigid inserts can limit both the design and the production of the whole insert when made using conventional, single-stage, injection-molded technologies. Additionally, when a change to a feature in the facepiece insert is needed, such as a different filter mount, a whole new mold must be provided to make the change. That is, a separate mold must be furnished for the whole nosepiece and not simply for a portion of it.